Powder spray booth

ABSTRACT

An electrostatic powder spray booth for facilitating the cleaning of the booth and the recovery of powder spray material. The booth has a bottom divided into troughs, each one of which is individually connected to a powder recovery system through a suction hose and manifold connection. Within each trough there is a baffle plate configurated so as to create a high velocity air stream along the side walls of the trough and an air turbulence chamber beneath the plate so that powder is swept from the side and bottom walls of the trough and out of the turbulence chamber into the powder recovery system. The baffle plates are adjustably mounted within the bottom troughs so that the velocity of the air stream over the side walls of the trough may be controlled and varied and the ports which connect the trough to the recovery system are adjustable in size so that the system may be balanced to maximize the cleansing effect of the suction air streams.

[ 1 June 4, 1974 1 POWDER SPRAY BOOTH [75] Inventors: Frank Rombach, Kraainem;

Cornelis N. Venlet, Brussels, both of Belgium [73] Assignee: Nordson Corporation, Amherst,

Ohio

[22] Filed: Apr. 26, 1973 [2]] Appl. N0.: 354,848

[52] US. Cl. 98/115 SB, 118/312, 118/634,

Primary E.taminer Meyer Perlin Assistant ExaminerHenry ,C. Yuen Attorney, Agent, or Firm-Wood, Herron & Evans [57] ABSTRACT An electrostatic powder spray booth for facilitating the cleaning of the booth and the recovery of powder spray material. The booth has a bottom divided into troughs, each one of which is individually connected to a powder recovery system through a suction hose and manifold connection. Within each trough there is a baffle plate configurated so as to create a high velocity air stream along the side walls of the trough and an air turbulence chamber beneath the plate so that powder is swept from the side and bottom walls of the trough and out of the turbulence chamber into the powder recovery system. The baffle plates are adjustably mounted within the bottom troughs so that the velocity of the air stream over the side walls of the trough may be controlled and varied and the'ports which connect the trough to the recovery system are adjustable in size so that the system may be balanced to maximize the cleansing effect of the suction air streams.

36 Claims, 7 Drawing Figures PATENTED Jllli 4 I974 SHEEI 2 BF Q POWDER SPRAY B The invention of this application relates to apparatus for electrostatically coating the surface of articles with dry pulverant materials or powders. More particularly,

. the invention of this application relates to an improved spray booth within which pulverant materials or powders are sprayed onto the articles.

Powder spraying of articles is now a common commercial practice for coating or painting articles without the use of conventional solvents and liquid paint carriers. The powder is applied to the article by entraining very small particles of the powder, generally in a size range between and 80 microns, within a low pressure air stream and directing that stream from an electrostatic powder spray gun toward the article. A high voltage electrical charge is applied to the powder at the nozzle of the spray gun, which charge then causes the particles to migrate toward and to adhere to the grounded object. Subsequently, the powder coating is heated and fused to the article in an oven.

One characteristic of electrostatic powder spraying is that a very high percentage of the total sprayed powder becomes overspray and fails to adhere to the article.

This overspray represents such a high percentage of the total quantity of sprayed powder that commercial utilization of the powder spraying technique dictates that the application equipment incorporate some form of powder recovery system. Conventionally that recovery system includes a spray booth within which the powder is sprayed onto the article and a suction system through which all of the overspray is withdrawn from the booth.

A common problem encountered with commercial electrostatic powder spray systems is the inconvenience and delay which attends a change in powder composition or powder color. In the event of such a change, the complete powder spray system, including the booth and recovery system, must be completely purged of the old pulverant material or powder in order to prepare it to spray the new. In the case of the powder spray booth, this is a time consuming and expensive operation which generally requires that the side and bottom walls of the booth be manually vacuumed in order to clean the surfaces of the booth of electrostatically charged and consequently adhered powder. Even a very minor amount of such powder if left in the booth can ruin subsequent production when mixed with a different color or composition powder material.

It has therefore been one objective of this invention to provide an improved powder spray booth which is self-cleaning and in which many of the surfaces of the booth remain free of powder and need never be manually cleaned upon a powder change.

Another common problem encountered in electrostatic spray systems is a safety problem which occurs in consequence of a build up of powder material inside the booth and particularly in the bottom of the booth. Such build ups are unsafe because of their potential as heaith, fire or explosion hazards. Therefore another objective of this invention has been to provide a powder spray booth which eliminates all surfaces upon which powder can settle or become deposited so as to give rise to a safety hazard.

These objectives are accomplished and this invention is partially predicated upon the concept of a booth so designed that there is a high velocity air flow over all surfaces upon which powder would otherwise tend to adhere or collect. Specifically, the invention of this application is partially predicated upon the concept of utilizing the suction air flow required to recover the oversprayed powder to create high velocity air flow currents over the inside surfaces of the booth upon which powder otherwise tends to settle.

To create these high velocity air flow streams while still maintaining low velocity air currents within the booth and around the product so as not to disturb or remove powder from the product, the invention of this application incorporates a plurality of troughs in the bottom of the booth and high velocity air flow creating baffles within each trough. In one preferred embodiment, each trough is generally W shaped when viewed in cross section and has aninverted V shaped baffle located within the trough. Flanges at theouter lower edges of the baffle function to create narrow air flow passages through which all suction air from the booth must pass. in the course of moving through these narrow passages, high velocity air flow streams are generated which then function to scrub or remove powder from the sides and bottoms of the troughs. In order to enhance powder removal from the bottoms of the troughs, channels at the very bottoms of the troughs are smoothly rounded and the high velocity air stream is so directed that it swirls around the bottoms of the channels and picks up powder which otherwise drops out and becomes deposited in the bottoms of the channels.

Still another aspect of the invention is predicated upon the adjustability of the high velocity air flow creating passages. This adjustability enables the velocity of the air stream along the side walls of the trough to be adjusted and varied. To this end the passage defining flanges of the baffles rest upon and are supported by adjustment screws which extend through the side walls of the trough. By varying the extent to which the adjustment screws extend into the trough, the width of the passage may be varied and thereby the velocity of the air flow over the inside walls of the trough.

Still another aspect of this invention is predicated upon the concept of dividing the bottom of the spray booth into individually separated troughs and balancing air flow from each separated section so that each is purged of powder by the air flow through that section. This balancing is effected by the provision of a plurality of apertured plates configurated to fit over openings in the bottoms of troughs which interconnect the trough to the exhaust system. Those apertured plates have different size openings so that by varying the size openings between individual sections of the trough it is possible to increase or decrease the air flow within each section and to use only so much flow within an individual section as is required to effectively evacuate that section.

Still another aspect of this invention resides in the creation of self-cleaning air flow patterns internally of an exhaust manifold which interconnects the bottom of the booth to a powder recovery system. It has been found that the manifold, which generally connects the individual bottom trough sections of the booth to the powder recovery system, can and often does serve as a trap where powder collects and is held until it is subsequently disturbed. Eventually though it breaks out of the manifold, often after a color or material change. To

prevent this build-up the powder spray booth of this application includes a main manifold connected to the individual sections of the troughs in the bottom of the booth through individual conduits or hoses, each one of which injects air entrained powder into the manifold in a tangential direction so that a spiral air flow pattern is achieved internally of the manifold. This spiralling air flow scrubs the interior of the manifold of powder and keeps it free of powder build-up.

These and other objects and advantages of this invention will be more readily apparent from the following description of the drawings in which:

FIG. 1 is a perspective view of the powder spray booth incorporating the invention of this application.

FIG. 2 is a cross sectional view through the booth taken on line 2-2 of FIG. 1.

FIG. 3 is a cross sectional view through the booth taken on line 3-3 of FIG. 1.

FIG. 4 is an exploded perspective view of a portion of the bottom of the booth of FIG. 1.

FIG. 5 is an exploded perspective view of a portion of the bottom of the booth.

FIG. 6 is a perspective view of a vacuum attachment to the booth.

FIG. 7 is a diagrammatic view of the powder spray system incorporating the invention of this application.

Referring first to FIGS. 1 and 7, there is illustrated a spray booth 10 which incorporates the invention of this application. This booth is conventionally used in an electrostatic powder spray system 5 which includes a powder recovery system for recovering and reconditioning oversprayed powder. Such an electrostatic spray system 5 is illustrated diagrammatically in FIG. 7 and includes electrostatic spray guns 11 and 12 from which air entrained powder is ejected toward an object or article 13 suspended in the booth from conveyorized hooks 14. As the powder, which normally has a particle size range between IO and 80 microns, is ejected from the guns 11 and 12, a high voltage charge is applied to the powder particles so as to cause them to migrate and attach to the grounded object 13. Subsequently, the powder coated object 13 is conveyed from the booth to an oven where the object is heated so as to cause the powdered particles to be fused onto the object 13.

One characteristic of electrostatic powder spray systems is that a high percentage of the particles ejected from the guns 11 and 12 does not migrate onto the object 13, but instead becomes overspray which is withdrawn by suction from the booth through conduits 17 into a suction manifold 18 and subsequently into the recovery system. In the illustration of FIG. 7 the powder recovery system includes a conventional recovery unit 19 in which the air withdrawn from' the booth 10 is caused to pass through filter bags 20 into an exhaust fan 21 and subsequently to atmosphere through a blower silencer 22. In the course of passing through the filter bags, the air entrained powder drops to the bottom of the powder recovery unit 19 where it is fluidized in a conventional fluidizing bed 25. From the fluidizing bed 25 the powder is moved by a pump 26 back to a conventional sieve 27 through a conduit 28. From the sieve 27 the recovered powder, less all foreign particles, such as dust, dirt and debris which may have been picked up by the suction air stream is ejected into a second fluidizing bed 23. From this last fluidizing bed 23 the clean powder is recirculated bypump 24 back to the spray guns 1]. and 12.

This powder recovery system 5 (FIG. 7) other than the booth 10, the conduits 17 and manifold 18, are all conventional in the prior art and form no part of the invention of this application. It has only been illustrated and described so as to facilitate an understanding of the operation of the invention of this application.

Referring now to FIGS. 1 and 3, it will be seen that the booth 10 comprises a pair of opposed side walls 30, 31, a pair of opposed end walls 32, 33, a topwall 34, and a bottom wall 35. The end walls 32, 33 and top wall 34 define a longitudinal slot through which conveyorized articles 13 pass while suspended from conveyorized hooks 14. In the course of passage through the booth, the articles suspended from the hooks pass between spray guns mounted in windows or apertures 38, 39 of the side walls 30, 31, respectively. In the preferred embodiment illustrated in FIG. 1, there are three windows in each side wall 30, 31 and a spray gun 11, 12 is mounted in each of the windows.

The bottom 35 of the booth is shaped as two long parallel troughs 40, 41 which extend for. the full length or between the ends 32, 33 of the booth. Each trough 40, 41 is divided into three sections of equal length by a pair of dividers 43, 44 which extend transversely across and between the side walls 30, 31. In the preferred embodiment these divider walls 43, 44 are shaped as an inverted V when viewed in cross section and slope at an angle of approximately 15 to 30 to a vertical plane. The slope is provided on these walls in order to minimize the quantity of electrostatically charged particles adhering to the divider walls.

Referring now to FIG. 2, it will be seen that each of the troughs 40, 41 is generally W shapedwhen viewed in cross section and that each is defined by a pair of downwardly and inwardly sloping sidewalls 47 and 48 joined to a pair of upwardly and inwardly sloping walls 49, 50. The side walls 47 and 48 define an angle a of approximately 35 with a vertical plane through the wall and the walls 49 and 50 define an angleB of approximately 50 relative to a vertical plane through the wall. In the preferred embodiment the juncture or the intersection between the side walls 47 and 48 and the walls 49, 50 respectively is rounded at the'bottom with a radius of curvature of approximately 6 millimeters so as to provide a smooth air flow path as is explained more fully hereinafter.

Located within each of three sections of each trough 40, 41 there is a removable baffle 52, 53, 54, 55, 56 and 57. These baffles are all identical and therefore only one, 52, will be illustrated and described in detail.

Each baffle 52 is generally shaped when viewed in cross section as an inverted V having side walls 59 and 60 which define an included angle C at the apex of approximately The end edges 61 of each baffle are cut so that the ends match the slope of the divider walls 43 and 44 and rest closely adjacent or against the sloping sides of the dividers 43, 44.

At its lower end, each baffle wall 59 and 60 has an inwardly turned flange 63, 64,'extending downwardly from it parallel to the side walls 47, 48 of the troughs. These flanges 63, 64 cooperate with the side walls 47, 48 of each trough to define an air flow passage 65, 66 for suction air withdrawn through openings 70, 71, 72, 73, 74,75 in the bottom of the sections of the troughs into the conduits l7 and subsequently into the powder recovery system. These passages 65, 66 are relatively narrow (6 millimeters in width w in one preferred embodiment) so that a high velocity air stream is created in the course of passage through the passages, which high velocity air stream is then directed by the flanges and side walls downwardly over and parallel to the inside surface of the side walls 47, 48. This high velocity air stream has the effect of washing or scrubbing powder from the lower inside surface 67, 68 of the side walls 47, 48 and from the rounded channels 45, 46 at the bottom of the troughs where the powder normally tends to collect and adhere. As the result of the inclusion of the baffles, those surfaces which are in the absence of the baffle covered with powder particles, sometimes to a depth of several inches at the bottom of the channels 45, 46, swept clean by the high velocity air stream.

in the preferred embodiment, the baffies 52, 57 are adjustably mounted in the trough so that the width of the passage 65, 66 and consequently the velocity of the air stream passing through the passage may be adjusted and controlled. This adjustment comprises four adjustment screws 80 threaded through each of the side walls 67, 48 against which the flanges 63, 64 of the baffles abut. In the preferred embodiment of the invention an optimal velocity through this passage has been found to be approximately 8,000 feet per minute, but an air stream velocity of anywhere from 5,000 to 10,000 feet per minute has been found to be operable.

The baffles 52-57 preferably also include handles 81 welded or otherwise secured to the top of the baffle to enable it to be lifted from the trough. Baffle removal is required to enable the air flow from each section of the trough to be adjusted relative to any other section as is explained more fully hereinafter. The baffles are also generally removable so as to enable the bottoms of the troughs to be completely cleaned upon a change of color or material utilized in the system.

Referring to FlGS. 2 and 5 it will be seen that the orifices 70-75 in the bottom of each section of the troughs 40, M are spaced upwardly from the bottom of the channels 45, 46. in one preferred embodiment of the invention, the lower edge of the orifices are spaced a distance D of approximately 20 millimeters from the bottoms of the channels 45, 46. This location of the ori fice has been found to be optimal for proper cleansing of the inside surfaces of the trough of powder and for maximum recovery of powder from the booth. As indicated by the arrows 85, 86 the high velocity air streams created by forcing all suction air flow to pass through the passages 65, 66 creates air streams which flow downwardly over the side walls 47, 48 of the troughs, over the bottom of the channels 45, 46 and upwardly again over the walls 49 and 50 in order to enter the opening 70. These air flow streams then create a turbulent flow of air beneath the baffle 52 which wash all of the powder from the underside of the baffles.

Optimal cleansing of the surfaces of the booth with the available air supply often requires greater air flow in one section beneath baffies 52-57 than in another. As an example, if an automatic spray gun is being utilized. at one end of the booth and a hand or manually operated touch up gun at the opposite end, there is a need for a greater exhaust air flow in the area where the majority of powder is being applied by the automatically operated gun. In that case, it is advantageous to be able to control the relative rates of exhaust air flow in the individual sections beneath baffles 52-57 of the troughs 40, 4B. To that end, a plurality of balance air flow means or tuning plates 90 having varying size apertures 911 are preferably utilized to cover the orifices -75 in the bottom of each section of the trough. These control plates are preferably angled so that they fit over and rest against the inside surface of the walls 49 and 50 in the bottom of each trough. Each plate has an aperture 91 therein which may be of the same or of a differing size from the aperture in the adjacent section of the trough. By varying the size aperture over each opening 70-75 it is possible to control or balance the relative quantity of exhaust air flow exhausted through each section and thereby tune the booth to insure maximum utilization of the available exhaust air.

The preferred embodiment of the invention also incorporates a vacuum hose attached to one of the adjustable orifice plates. The vacuum hose 94 mounted in the aperture 95 of the cover plate 93 enables that cover plate to be mounted over any one of the orifices 70-75 so as to attain a vacuum to clean the side walls of the booth directly from the powder recovery suction air flow. All that is required to use this vacuum attachment is to locate the plate 93 over any one of the orifices 70-75, cover with non-apertured plates so many of the other orifices 70-75 as is necessary to obtain the desired vacuum at the orifice of the vacuum plate 93, and then move the nozzle 96 secured to the flexible hose 94 over the surface to be cleaned.

So long as the exhaust fan 21 (FIG. 7) is operated, exhaust air is pulled from the booth l0 downwardly through the passages 65 and 66 defined by the baffles and into the conduits 17. These conduits then transmit the suction air with the entrained overspray powder to an exhaust manifold 18. In the preferred embodiment the exhaust manifold has a flow capacity equal to or slightly greater than the total flow capacity of the six conduits 17 which interconnect the manifold 18 to the orifices 70-75 in the bottom of the sections of the troughs 40, 41. It is to be noted that the main exhaust manifold is mounted on one side of the booth spaced a substantial distance from the orifices 74, which are most closely linked to it.

Referring to FIG. 2 it may be seen that the entry ports of the conduits 17 into the exhaust manifold 18 are all located tangentially relative to the circular cross section manifold. This tangential location of the entry ports from the conduits into the exhaust manifold has been found to create a spiral air flow within the exhaust manifold 18, which spiral air flow may continue for as much as 40-50 feet from the point of entry of the conduits into the exhaust manifold and eliminates the accumulation of powder on the inside of the manifold 18. In the absence of this tangential introduction of air flow into the manifold, a buildup of powder occurs adjacent the openings from the conduit 17 into the manifold 18.

To operate the system illustrated in FIG. 7, the exhaust fan 21 is started so as to cause suction air to be pulled from the spray booth downwardly through the troughs 40, 41 into the orifices 70-75 at the bottom of the troughs. This exhaust air is then pulled through the conduits 17 into the exhaust manifold 18 and subsequently back to the bag filter 19, from which the air is exhausted through the fan and a blower silencer 22. Powder having a particle size of from 10 to microns is introduced into the fluidized bed 23 and the pump 24 started. This purnpthen causes powder entrained air to be transmitted to the electrostatic spray guns it and 12 from which electrostatically charged particles are ejected toward an object 13 contained within the booth. The electrostatically charged particles then migrate onto the electrically grounded object 13, but a large percentage of the powdered material ejected from the guns ll, 12 fails to adhere to the object and becomes overspray. These oversprayed particles are withdrawn by the suction air flow downwardly into the troughs 40, 41 with the suction air flow. This suction air flow, the quantity of which is controlled by the capacity of the exhaust fan 21, and in one preferred embodiment is equal to approximately 2,100 cubic feet per minute, is then caused to flow downwardly through the restrictions provided by the passages 65 located between the inside walls 47, 48 of the trough and the flanges 63, 64 of the baffle. In the preferred embodiment, this air flow stream reaches a velocity of approximately 8,000 feet per minute in the course of passing through the passages 65, 66. As the air flow is ejected from the passages it forms a high velocity air stream which cleans the powder from the inside surface 73, 74 at the bottom of the trough and picks up and removes all powder from the bottoms of the channels 45, 46 of the troughs. This air flow then creates a turbulent air flow pattern beneath the baffles 52-57, which turbulent air flow maintains the powder in entrainment in the in the air stream until it is pulled through the orifices 70-75 at the bottom of each section of the trough into the conduits 17. From the conduits 17, the suction air entrained powder is transmitted to the exhaust manifold l8 and subsequently back to the filter 19. At the filter, the entrained powder drops downwardly into a fluidized bed while the exhaust air passes through filter bags 20 back out through the exhaust fan. A pump '26 then transmits the powder from the fluidized bed 25 back to the sieve 27 and subsequently into the supply fluidizing bed 23 for return to the spray guns.

While I have described only one preferred embodiment of my invention, persons skilled in the powder spray art will appreciate numerous changes and modifications which may be made without departing from the spirit of my invention. Similarly, persons skilled in the art will appreciate that the principles of the invention described and claimed herein may be embodied in systems having different flow rates and air flow velocities without departing from the spirit of my invention. Therefore I do not intend to be limited except by the scope of the following appended claims.

Having described my invention, 1 claim: l. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having at least one opening, said bottom wall opening being adapted to establish communication between the interior of said booth and a pulverant material recovery system,

said bottom wall defining at least one generally open top trough having downwardly and inwardly sloping side walls, and

means for generating a high velocity air stream directed downwardly along the side walls of said trough to sweep pulverant material from said side walls, said high velocity air stream generating means including a baffle located within said trough, said baffle having generally upwardly and inwardly sloping side walls and having bottom edges spaced from but located closely adjacent the inside surface of said trough side walls so as to define a high velocity air flow passage between each of said baffle bottom edges and said trough side walls.

2. The spray booth of claim 1 in which said baffle is generally shaped as an inverted V when viewed in cross section. I

3. The spray booth of claim 1 in which said baffle has a flange along each of its bottom edges, said flanges extending generally parallel to said side walls of said trough and being operable to direct air flow through said air flow passages and parallel to said side walls of said trough.

4. The spray booth of claim 1 in which said baffle has a handle attached and is portable and removable from said trough for purposes of cleaning said booth.

5. The spray booth of claim 1 in which said trough is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels at the bottom of said trough, each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.

6. The spray booth of claim 5 in which said bottom wall opening of said booth is located between said two bottom channels of said trough and has its peripheral edge spaced upwardly from the bottom of each of said channels.

7. The spray booth of claim 3 in which said trough is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels atthe bottom of said trough,-each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.

8. The spray booth of claim 1 which further includes means to adjust the velocity of air flow in said air flow passages.

9. The spray booth of claim 1 in which said bottom wall includes a plurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system,

said booth further including an exhaust manifold havinga smoothly curved inside surface,

a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold,

a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.

10. The spray booth of claim 9 in which said inside surface of said exhaust manifold is circular.

11. The spray booth of claim 10 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold.

12. The spray booth of claim 1 which includes a plurality of open top troughs defined by said bottom wall and a plurality of bottom wall openings, each of said bottom wall openings entering into one of said troughs, said booth further including means to balance air flow from said openings so as to enable the quantity of air pulled through each opening into the pulverant material recovery system to be adjusted relative to the quantity pulled through any other opening.

13. The spray booth of claim 12 in which said air flow balancing means includes a plurality of plates having varying size openings therein and shaped so as to fit over said bottom openings.

14. The spray booth of claim 13 which further includes a vacuum attachment for cleaning said booth, said attachment comprising a vacuum plate having an opening therein, and

shaped so as to fit over said bottom openings,

a vacuum hose sealingly connected at one end to said opening in said vacuum plate, and

a vacuum pick up nozzle sealingly attached to the opposite end of said hose.

15. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having at least one opening, said opening being adapted to establish communication between the interior of said booth and a pulverant material recovery system,

said bottom wall defining at least one generally open top trough having downwardly and inwardly sloping side walls, and

a baffle located within said trough, said baffle having generally upwardly and inwardly sloping side walls and having a flange along each of its bottom edges which extends parallel to and is spaced from said side walls of said trough so as to define passages for directing air flow parallel to and along said side walls of said trough so as to sweep pulverant material from said side walls.

16. The spray booth of claim 15 in which said trough is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels at the bottom of said trough, each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.

17. The spray booth of claim 16 in which said bottom wall opening of said booth is located between said two bottom channels of said trough and has its peripheral edge spaced upwardly from the bottom of each of said channels.

R3. The spray booth of claim 15 which further includes means for adjusting the clearance between said flanges of said baffle and said side walls of said trough so as to enable the velocity of air passing through said channels to be varied.

19. The spray booth of claim 18 in which said adjusting means includes screws which are threaded through said side walls and abut against said flanges of said baffle.

20. The spray booth of claim 15 in which said bottom wall includes aplurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system,

said booth further including an exhaust manifold having a smoothly curved inside surface,

a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold,

a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.

21. The spray booth of claim 20 in which said inside surface of said exhaust manifold is circular.

22. The spray booth of claim 21 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold.

23. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having at least one opening for establishing communication between the interior of said booth and a pulverant material recovery system,

said bottom wall defining at least one generally long open top trough which is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels at the bottom of said trough, each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.

24. The spray booth of claim 23 in which said bottom wall opening of said booth is located between said two bottom channels of said trough and has its peripheral edge spaced upwardly from the bottom of each of said channels.

25. The spray booth of claim 23 in which said bottom wall includes a plurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system,

said booth further including an exhaust manifold having a smoothly curved inside surface,

a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold,

a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.

26. The spray booth of claim 25 in which said inside surface of said exhaust manifold is circular.

27. The spray booth of claim 26 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold.

28. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having a plurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system,

said booth further including an exhaust manifold having a smoothly curved inside surface,

a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold,

a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.

29. The spray booth of claim 28 in which said inside surface of saidexhaust manifold is circular.

30. The spray booth of claim 29 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold. 30

31. The spray booth of claim 28 which includes a plurality of open top troughs defined by said bottom wall, each of said bottom wall openings entering said one of said troughs, said booth further including balancing means includes a plurality of plates having a vacuum hose sealingly connected at one end to said opening in said vacuum plate, and

a vacuum pick up nozzle sealingly attached to the opposite end of said hose.

34. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having a plurality of bottom wall openings, said bottom wall openings being adapted to establish communication between the interior of said booth and a pulverant material recovery system, and

means to balance air flow from said openings so as to enable the quantity of air pulled through each opening into the pulverant material recovery system to be adjusted relative to the quantity pulled through any other opening.

35. The spray booth of claim 34 in which said air flow balancing means includes a plurality of plates having varying size openings therein and shaped so as to fit over said bottom openings.

36. The spray booth of claim 35 which further includes a vacuum attachment for cleaning said booth, said attachment comprising a vacuum plate having an opening therein, and

shaped so as to fit over said bottom openings,

a vacuum hose sealingly connected at one end to said opening in said vacuum plate, and

a vacuum pick up nozzle sealingly attached to the opposite end of said hose. 

1. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having at least one opening, said bottom wall opening being adapted to establish communication between the interior of said booth and a pulverant material recovery system, said bottom wall defining at least one generally open top trough having downwardly and inwardly sloping side walls, and means for generating a high velocity air stream directed downwardly along the side walls of said trough to sweep pulverant material from said side walls, said high velocity air stream generating means including a baffle located within said trough, said baffle having generally upwardly and inwardly sloping side walls and having bottom edges spaced from but located closely adjacent the inside surface of said trough side walls so as to define a high velocity air flow passage between each of said baffle bottom edges and said trough side walls.
 2. The spray booth of claim 1 in which said baffle is generally shaped as an inverted V when viewed in cross section.
 3. The spray booth of claim 1 in which said baffle has a flange along each of its bottom edges, said flanges extending generally parallel to said side walls of said trough and being operable to direct air flow through said air flow passages and parallel to said side walls of said trough.
 4. The spray booth of claim 1 in which said baffle has a handle attached and is portable and removable from said trough for purposes of cleaning said booth.
 5. The spray booth of claim 1 in which said trough is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels at the bottom of said trough, each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.
 6. The spray booth of claim 5 in which said bottom wall opening of said booth is located between said two bottom channels of said trough and has its peripheral edge spaced upwardly from the bottom of each of said channels.
 7. The spray booth of claim 3 in which said trough is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels at the bottom of said trough, each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.
 8. The spray booth of claim 1 which further includes means to adjust the velocity of air flow in said air flow passages.
 9. The spray booth of claim 1 in which said bottom wall includes a plurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system, said booth further including an exhaust manifold having a smoothly curved inside surface, a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold, a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.
 10. The spray booth of claim 9 in which said inside surface of said exhaust manifold is circular.
 11. The spray booth of claim 10 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold.
 12. The spray booth of claim 1 which includes a plurality of open top troughs defined by said bottom wall and a plurality of bottom wall openings, each of said bottom wall openings entering into one of said troughs, said booth further including means to balance air flow from said openings so as to enable the quantity of air pulled through each opening into the pulverant material recovery system to be adjusted relative to the quantity pulled through any other opening.
 13. The spray booth of claim 12 in which said air flow balancing means includes a plurality of plates having varying size openings therein and shaped so as to fit over said bottom openings.
 14. The spray booth of claim 13 which further includes a vacuum attachment for cleaning said booth, said attachment comprising a vacuum plate having an opening therein, and shaped so as to fit over said bottom openings, a vacuum hose sealingly connected at one end to said opening in said vacuum plate, and a vacuum pick up nozzle sealingly attached to the opposite end of said hose.
 15. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having at least one opening, said opening being adapted to establish communication between the interior of said booth and a pulverant material recovery system, said bottom wall defining at least one generally open top trough having downwardly and inwardly sloping side walls, and a baffle located within said trough, said baffle having generally upwardly and inwardly sloping side walls and having a flange along each of its bottom edges which extends parallel to and is spaced from said side walls of said trough so as to define passages for directing air flow parallel to and along said side walls of said trough so as to sweep pulverant material from said side walls.
 16. The spray booth of claim 15 in which said trough is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels at the bottom of said trough, each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.
 17. The spray booth of claim 16 in which said bottom wall opening of said booth is located between said two bottom channEls of said trough and has its peripheral edge spaced upwardly from the bottom of each of said channels.
 18. The spray booth of claim 15 which further includes means for adjusting the clearance between said flanges of said baffle and said side walls of said trough so as to enable the velocity of air passing through said channels to be varied.
 19. The spray booth of claim 18 in which said adjusting means includes screws which are threaded through said side walls and abut against said flanges of said baffle.
 20. The spray booth of claim 15 in which said bottom wall includes a plurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system, said booth further including an exhaust manifold having a smoothly curved inside surface, a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold, a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.
 21. The spray booth of claim 20 in which said inside surface of said exhaust manifold is circular.
 22. The spray booth of claim 21 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold.
 23. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having at least one opening for establishing communication between the interior of said booth and a pulverant material recovery system, said bottom wall defining at least one generally long open top trough which is generally W shaped when viewed in cross section so as to define a pair of generally parallel channels at the bottom of said trough, each channel being rounded at the bottom so as to provide a smoothly curved air flow path for a high velocity stream of air directed downwardly over the inside surface of the side walls of said trough.
 24. The spray booth of claim 23 in which said bottom wall opening of said booth is located between said two bottom channels of said trough and has its peripheral edge spaced upwardly from the bottom of each of said channels.
 25. The spray booth of claim 23 in which said bottom wall includes a plurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system, said booth further including an exhaust manifold having a smoothly curved inside surface, a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold, a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.
 26. The spray booth of claim 25 in which said inside surface of said exhaust manifold is circular.
 27. The spray booth of claim 26 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold.
 28. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed iNto the interior of said booth and said bottom wall having a plurality of openings for establishing communication between the interior of said booth and a pulverant material recovery system, said booth further including an exhaust manifold having a smoothly curved inside surface, a plurality of entrance ports into said exhaust manifold, each of said entrance ports being tangentially located relative to said curved inside surface of said exhaust manifold, a plurality of fluid conduits, each of said conduits connecting one of said bottom openings to one of said entrance ports of said exhaust manifold and being so sized and directed that pulverant material is introduced tangentially into said exhaust manifold from said conduits.
 29. The spray booth of claim 28 in which said inside surface of said exhaust manifold is circular.
 30. The spray booth of claim 29 in which said exhaust manifold entrance ports are circular and have a diameter which is no more than one-half the inside diameter of said exhaust manifold.
 31. The spray booth of claim 28 which includes a plurality of open top troughs defined by said bottom wall, each of said bottom wall openings entering said one of said troughs, said booth further including means to balance air flow from said openings so as to enable the quantity of air pulled through each opening into the pulverant material recovery system to be adjusted relative to the quantity pulled through any other opening.
 32. The spray booth of claim 31 in which said air flow balancing means includes a plurality of plates having varying size openings therein and shaped so as to fit over said bottom openings.
 33. The spray booth of claim 32 which further includes a vacuum attachment for cleaning said booth, said attachment comprising a vacuum plate having an opening therein, and shaped so as to fit over said bottom openings, a vacuum hose sealingly connected at one end to said opening in said vacuum plate, and a vacuum pick up nozzle sealingly attached to the opposite end of said hose.
 34. A spray booth for use in the coating of objects with pulverant material and for facilitating the recovery of surplus pulverant material, which booth comprises side walls, end walls, and a bottom wall, at least one of said side walls having an opening for a spray gun directed into the interior of said booth and said bottom wall having a plurality of bottom wall openings, said bottom wall openings being adapted to establish communication between the interior of said booth and a pulverant material recovery system, and means to balance air flow from said openings so as to enable the quantity of air pulled through each opening into the pulverant material recovery system to be adjusted relative to the quantity pulled through any other opening.
 35. The spray booth of claim 34 in which said air flow balancing means includes a plurality of plates having varying size openings therein and shaped so as to fit over said bottom openings.
 36. The spray booth of claim 35 which further includes a vacuum attachment for cleaning said booth, said attachment comprising a vacuum plate having an opening therein, and shaped so as to fit over said bottom openings, a vacuum hose sealingly connected at one end to said opening in said vacuum plate, and a vacuum pick up nozzle sealingly attached to the opposite end of said hose. 